How to launch native email with an image

OK, so I suppose this is perhaps the best option. I tried this plugin

https://github.com/katzer/cordova-plugin-email-composer/blob/cab303d/README.md

And the code is very straightfoward:

 var img_data = $scope.canvas.toDataURL("image/png");
 var options = { attachments: [ $scope.canvas.toDataURL("image/png") ], 
          subject: 'Enjoy!', body: 'See', isHtml: true};
 $cordovaEmailComposer.open(options);

Which asks which email app to use. But it does not attach the picture to email, says "Couldn't attach file." in gmail, and just nothing in outlook.

What am I missing? Thanks.